Method for converting c6 and higher aliphatic hydrocarbons to aromatics using as catalyst a free alkali metal on a carrier



United States Patent M IVE'I'HOD FOR CONVERTING C AND HIGHER ALIPHATIC HYDROAONS T0 AROMATIQS USING AS CATALYST A FREE ALKALI METAL ON A CR Patrick W. Ryan, Chicago Heights, Ill., assignor to Sinclair Research, Inc., Wilmington, Dcl., a corporation of Delaware No Drawing. Filed Aug. 13, 1962, Ser. No. 216,312

7 Claims. (Cl. 260673.5)

The present invention relates to the conversion of CH- aliphatic hydrocarbons to aromatics in the presence of a novel dehydrocyclization catalyst.

The catalytic conversion of C +hydr0carbons to aromatics is a reaction well known to the art. In addition to producing a desirable aromatics the reaction also has particular applicability to the upgrading of low octane paraflinic feedstocks commonly available to the refiner, to higher octane motor fuel components. A variety of catalysts have been employed for this reaction, for example, noble metals on alumina, chromina-alumina, and molybdena-alumina. These and other catalysts often suggested are, however, relatively expensive and the extent of side reactions effected by many of these catalysts seriously limits the selective yields of the desired aromatics.

It has now been discovered that paratiins and/or olefins having a straight chain of at least six carbon atoms can be converted to excellent yields of aromatics by contacting them under dehydrocyclization conditions with a catalyst consisting essentially of catalytic amounts of a free alkali metal on an alkali metal ion-containing solid support. The dehydrocyclization reaction is preferably carried out at atmospheric pressure but subatmospheric and superatmospheric pressures can be employed as well. The contact time or liquid hourly space velocity will be dependent on the particular catalyst, temperature and pressure employed but will generally range from about 0.05 to 10 LHSV, preferably about 0.1 to 1 LHSV with olefin feeds and about 0.1 to 0.2 with paraflins. The temperature employed lies generally in the range of about 600 to 1000 F. but the best conditions are dependent on the feed. When paraflin feeds are used the temperature employed is preferably about 900 to 1000 F., advantageously about 950 to 990 F. Conversion temperatures employing olefin feeds on the other hand more normally range from about 600 to 1000 F., preferably about 750 to 850 F.

The feeds of the present invention can be a paraffin or monoolefin having at least six up to about 12 carbon atoms or more and include branched chain parafiins and olefins, that is, having a straight chain length of at least 6 carbon atoms. The preferred feeds are those whose straight carbon chain length is of about 8 to 10 carbon atoms. The feed converted in accordance with the method of the present invention can be the paraffins or olefins per se, admixtures of the paraflins and olefins or feeds containing the same. Particularly suitable feeds are the low octane paraflinic feedstocks such as petroleum naphtha. It has been found, moreover, that the presence of paraflins and olefins which do not have at least six straight chain carbon atoms will not unduly affect the reaction of the present invention. Likewise, the presence of aromatics and naphthenes in the feedstock have little if any detrimental efiect 0n the conversion of the feeds of the present invention.

The catalyst of the present invention can be prepared by depositing a free alkali metal on a solid support that 3,240,832 Patented Mar. 15,1966

contains alkali metal ions, the amount of said alkali metal ions being sufiicient to at least neutralize the acidic sites on the support. The ions can be supplied by pretreatment of the support With alkali metal compounds or these compounds per se, e.g., K CO or K 50 could even serve as the support. The pretreatment of the support can be conducted, for example, by impregnation with solutions of alkali metal compounds, as, for instance, aqueous solutions of water-soluble alkali metal compounds including alkali metal compounds that de-. compose under elevated temperatures as, for instance drying or calcining temperatures. Suitable alkali metal compounds include, for instance, potassium, sodium, lithium, cesium and rubidium, alcoholates, chelates, hydroxides, carbonates, bicarbonates and salts of other weak acids or salts of strong acids that are at least partially soluble or decomposable at elevated temperatures. In most cases, the pretreatment with the alkali metal compound will be followed by heating at elevated temperature which can be calcining temperature, usually about 400 to 1300 F. or more, either to decompose the alkali metal compound and/or drive-off water. The amount of alkali metal compound employed, as aforementioned, is at least sufiicient to neutralize the normally acidic inert supports but amounts that provide a basic support are preferred. Whether the alkali metal ions serve as the support or are on another solid support, the resulting carrier for the free alkali metal to be added is non-acidic and is preferably baisc. Generally the amounts of alkali metal treating compounds employed on a support are those providing about 0.5 to 20%, preferably about 1 to 5%, of the alkali metal ion.

The free or elemental alkali metal constituent of the catalyst, i.e., K, Na, Li, Cs and Rb, can be dispersed on the alkali metal ion-containing support by any means known to the art. For example, the alkali metal ioncontaining support can be stirred with molten alkali metal in the presence or absence of an inert solvent at a temperature slightly above the melting point of the alkali metal. A combination of alkali metals can be employed, if desired. Catalytically effective amounts of free alkali metal are used and generally fall within the range of about 1 to 20% by weight, preferably about 1 to 10% by weight, of the catalyst. The preferred alkali metal is potassium.

Although the preferred support of the present invention is alumina, other normally acidic supports such as silica, silica-alumina, acid-treated diatomaceous earth, etc. are also suitable. The alumina can be any of the variety of available alumina or alumina hydrates such as the various forms of gamma family or activated alumina, etc.

The following examples are included to further illustrate the present invention.

EXAMPLE I A catalyst composed of 2.4 weight percent potassium metal dispersed on a 7 weight percent K+alumina support was charged to a 1" Universal reactor by adding a n-heptane-catalyst slurry under a blanket of nitrogen. The heptane was allowed to drain from the reactor and the temperature was raised to 975 F. under a slow stream of nitrogen.

A series 'of five runs was made on this catalyst with n-octane as the feedstock. The conditions and results of these runs are shown in Table I.

Table I Run No. 1242 35 36 37 38 39 Conditions 9' 5 F., Atmospheric Pressure, 0.1 LHSV Run time (hrs):

Prerun 1 1 1% /2 Run 51 4% 5% 6 6 Recovery g. (wt. percent):

7. 67 7. 81 7. 46 5. 93 9. 70 10. 57 9. 25 6. 99 26. 0 7.95 13.02 13. 13 1. 82 1. 46 1. 21 1. 03 3. 74 2. 75 2. 21 1. 75 o-Xylene 7. 85 31. 17 16. 13 15. 93

Total aromatics 15. 56 33. 83 48. 71 49. 28 44. 76

Conversion, percent- 39. 4 63. 3 71. 4 79. 4 77. 9 Selectivity, percent" 22. 0 30. 6 36. 2 34. 5 32. 2

1 The total coke on catalysts was divided proportionately over the five runs.

The data of Table I demonstrates the advantageous pentane or aromatic formation was found. Trace yields of aromatics obtained by the process of the present invention. As can be seen from the results after the catalyst comes up to activity (about hrs. to hrs. on stream), see Run 38, about 80 weight percent conversion of n-octane is obtained with a selectivity to aromatics of approximately EXAMPLE II Passage of n-hexane over a K/K+/Al O catalyst prepared as in Example I was carried out at 975 F., atmospheric pressure, and 0.1 liquid hourly space velocity.

amounts of piperylenes were found.

EXAMPLE IV To determine the non-catalytic behavior of hydrocarbons such as n-octane under these conditions a thermal run was made at 975 F., atmospheric pressure, and 0.1 liquid hourly space velocity with tabular alumina in place of the catalyst. A 99.9 Weight percent recovery was obtained. Analysis of the product showed 87% to be unreacted n-octane, 0.3% toluene, 0.6% benzene and the remainder lower molecular weight hydrocarbons.

EXAMPLE V This catalyst had previously been used in runs in which n-octane and toluene were utilized as feedstocks. The Passage of 42 g. of o-xylene over the K/K+/Al O results of two runs are given in Table II. catalyst of Example I, which had previously been used to process octane feedstock, at 900 F., atmospheric pres- T bl 11 sure, 0.2 LHSV with a nitrogen diluent resulted in the NHEXANE OVER KO/K H A1203 45 recovery of 38 g. of material which was essentially unchanged o-xylene. 1242 42 l 43 EXAMPLE VI Passage of 28 g. of methylcyclopentane over the same Catalyst K/ -l h a -l z catalyst and under the same conditions as Example V fifg fig $89; resulted in the recovery of 24 g. of liquid product. Ex- Feed, g 50.2 cept for trace amounts of probably methylcyclopentene g g g'ziggf i'fii percent) 63 $73 41 57?; the product was unchanged starting material. Wt. percent recovery 88. 8 91. 6

PRODUCT DISTRIBUTION BY V.P.C. AND 1\'I.S., G. PRODUCT/G. OF FEED G. unaccounted for 1 1 Coke is not taken into account in these two figures. 2 Vapor phase chromatography.

A catalyst composed of 2.4% K metal dispersed on a 7 weight percent K+/Al O support was charged to a 1" Universal reactor by passing a n-heptane catalyst slurry under a blanket of nitrogen. The heptane was drained and the catalyst brought to reaction temperature under a slow stream of nitrogen.

A series of four runs (Runs 29-32) in which mixed n-octenes were utilized as feedstock was carried out. The reaction was followed by taking grab samples at various BMQSS Spectmbcopy' times during each run to note the change in product distribution. No attempt was made to trap out condensable EXAMPLE HI gases. The estimated liquid recovery range is about Over the same catalyst used in Example II, 17.1 g. 2- 85-90%. pentene was run at 975 F., atmospheric pressure a d 0,1 Analyses of the grab samples for these runs are shown liquid hourly space velocity. The product consisted of 7 in Table IH. From the results shown, this catalyst sys- 11.5 .g. of liquid product and 2.1 g. of non-condensable tern has high activity for the conversion of octenes to gas. Analysis by vapor phase chromatography and mass aromatics. Based on vapor phase chromotography of spectroscopy showed the product to consist of hydrogen, the grab samples, there is a 63% by weight conversion of olefins, and parafiins in the H C range. Only a trace the olefin to 61.5 weight percent aromatics. The selecof C material was produced. No evidence for cyclotivity to C aromatics is also quite high. The catalyst 2030208 7 026 1 4 m3 4-2 5 2 5 & 4 1

289502 9 799 0 Q0 2 L& 7 6 3 4 1 2. The method of claim 1 wherein the feedstock is an olefin of 6 to 12 total carbons and the dehydrocyclization conditions include temperatures of about 600 to 1000" F.

3. The method of claim 1 wherein the feedstock is a parafiiu of 6 to 12 carbon atoms and the dehydrocyclization conditions include temperatures of about 900 to 1000 F.

4. The method of claim 1 wherein the amount of free alkali metal on the support is about 1 to by weight d the amount of alkali metal ion is about 0.5 to 20%.

5. The method of claim 2 wherein the alkali metal is potassium.

6. The method of claim 5 wherein the catalyst support is alumina.

7. The method of claim 6 wherein the feedstock is octene.

Atmospheric Pressure, 0.2 LHSV, N; diluent (2/1 Ng/HC mole ratio) EXAMPLE VIII he temperature was raised to [0 an appears to age after the first hour and then levels off with A further run (Run 38) was made in which 34.3 g. 5 of l-octene was passed over the catalyst of Example VII after it had been used in runs in which methylcyclopentane, o-xylene and n-octane were employed as feedstock.

catalyst age, is still quite active for this dehydrocycliza- 15 only a slow rate of aging.

The conditions for this run were the same as those cited in Example VII except that t 900 F. 28 g. of liquid product and 0.23 ft. of gas were collected. Vapor phase analyses of the liquid product is also shown in Table III as can be seen from these re sults, the catalyst, although it becomes less selective with tion reaction.

1 No attempt was made to difierentiate between the paralfins and olefins of each carbon number. 2 Probably Cg naphthenes. I claim: References Cited by the Examiner 1. A mfithod f0! the COnVEISiOIl of C6 plus aliphatic hydrocarbons to aromatics which comprises contacting a 1 729 943 V1929 H f 208 208 f at k 1 t d f th 't f r flins 0 Sass 68 S 06 Se 60 6 Tom e group Consls mg 0 P 3 2,034,068 3/1936 Wait nnnuuu" 2,058,534 10/1936 Wait 208208 2,059,542 11/1936 Wait 208208 ALPHONSO D. SULLIVAN, Primary Examiner.

JOSEPH R. LIBERMAN, Examiner.

and monoolefins having a straight carbon chain length of at least six carbon atoms under dehydrocyclization conditions with a catalyst consisting essentially of catalytically efiective amounts of a free alkali metal on a solid, acidic catalyst support selected from the group consisting of silica, alumina, and mixtures thereof containing suflicient alkali metal ions, to provide a non-acidic support. 

1. A METHOD FOR THE CONVERSION OF C6 PLUS ALIPHATIC HYDROCARBONS TO AROMATICS WHICH COMPRISES CONTACTING A FEEDSTOCK SELECTED FROM THE GROUP CONSISTING OF PARAFFINS AND MONOOLEFINS HAVING A STRAIGHT CARBON CHAIN LENGTH OF AT LEAST SIX CARBON ATOMS UNDER DEHYDROCYCLIZATION CONDITIONS WITH A CATALYST CONSISTING ESSENTIALLY OF CATALYTICALLY EFFECTIVE AMOUNTS OF A FREE ALKALI METAL ON A SOLID, ACIDIC CATALYST SUPPORT SELECTED FROM THE GROUP CONSISTING OF SILICA, ALUMINA, AND MIXTURES THEREOF CONTAINING SUFFICIENT ALKALI METAL IONS, TO PROVIDE A NON-ACIDIC SUPPORT. 